Uniformly-sized resin particles have been applied to various uses, such as electrophotographic toner particles, spacer particles for liquid crystal panels, colored particles for electric papers, and particles for supporting medical or pharmaceutical agents. Uniformly-sized resin particles are obtainable by, for example, soap-free polymerization that is induced in liquids. Soap-free polymerization desirably produces small-sized particles with a narrow size distribution and nearly spherical shape. However, because the soap-free polymerization is generally induced in water, it is inefficient to remove the water to collect the resultant resin particles. The soap-free polymerization requires a long time period until the reaction is terminated, and further requires another time period for separating the resultant particles from the liquid and washing and drying them repeatedly. Thus, the soap-free polymerization wastes large amounts of time, water, and energy.
Japanese Patent Application Publication No. 2008-286947 discloses a method of manufacturing toner. In this method, a toner constituents liquid is discharged from multiple nozzles formed on a thin film. The thin film is periodically and vertically vibrated by a vibration generator. In accordance with the periodical vibration of the thin film, the inner pressure of a liquid chamber to which the thin film is provided is also periodically varied and thus the toner constituents liquid is discharged from the liquid chamber to a gas phase to be formed into liquid droplets. Each liquid droplet thus discharged moves in the same direction in line within the gas phase. The liquid droplets are formed into spherical particles due to the difference in surface tension between the liquid droplets and the gas phase, and further dried into solid particles.
While the liquid droplets move in the same direction, an air current is generated around the liquid droplets because the gas phase that is viscous is given the speed of the moving liquid droplets. This air current is hereinafter referred to as accompanying air current. When the accompanying air current is generated around one line of the liquid droplets, the moving speed of the liquid droplets is gradually reduced by the action of the accompanying air current and viscosity of the gas phase. Because of having a different size, each liquid droplet in the line has a different moving speed. Therefore, the distance between the adjacent liquid droplets becomes smaller and smaller and the adjacent liquid droplets finally get coalesced. The coalesced liquid droplets accelerate coalescence of the subsequent liquid droplets because of having a greater fluid drag and a lower moving speed. This phenomenon in which liquid droplets get coalesced in the direction of movement is hereinafter referred to as vertical coalescence. In the gas phase, liquid droplets which have been vertically coalesced and those which have not been coalesced are coexisting. Therefore, the resulting particles have various sizes, which is not suitable for toner particles.